It is well known that thermoplastic articles formed from a variety of polyolefin-containing plastic materials have widely varying surface properties, including surface tension, roughness and flexibility. As substrates used in forming a bonded composite, achieving durability, i.e., environmentally-resistant bonding has been a continuing challenge. There are many known adhesion promoters used as tie-coats, or primers for paints on polyolefin-based materials. Applying a tie coat is normally an added step in the coating process. The adhesion promoter is usually applied in a thin layer, normally about 6 to 10 microns (μm).
Known adhesion promoters for coatings olefin-based thermoplastic surfaces contain chlorinated polyolefins, some examples of which are described in U.S. Pat. Nos. 4,997,882; 5,319,032 and 5,397,602. Others include carboxy-modified polyolefins. See U.S. Pat. No. 4,299,754 teaching carboxylate-modified polyolefins in aromatic or aliphatic hydrocarbon or a chlorinated hydrocarbon.
Performance obtained with chlorinated polyolefin in tie-layers for coatings is not predictive for bonding of olefin-based articles to substrates typically encountered, such as steel and aluminum. This is demonstrated in an article in the Journal of Coating Technology, 65, No. 827 p. 21 (1993) for chlorinated polyolefins.
In the case bonding rigid substrates in-line to a molten olefin-based thermoplastic profile or in insert-injection molding, temperatures above the processing temperature or heat dwell times must be avoided. Melt-processible thermoplastic elastomers, or TPE's, TPV's, TPO's (hereinafter collectively, “TPE”) are desirable materials for forming such products as window channels, weatherstrips, and various automobile trim pieces. A rigid, structural substrate such as metal or rigid thermoplastic is joined in-line to the molten profile. In similar fashion, there are known methods where a rigidifying substrate and TPE are joined by insert injection molding. Improved adhesion between the substrate and TPE is desired.
U.S. Pat. No. 5,051,474 to Warren, et al discloses adhesives comprising a linear polyester polyurethane, a halogenated polyolefin, a phenolic resin, and a cross-linker. The formulation is preferably utilized as a two-component adhesive for bonding polymer blend-based thermoplastic elastomers to various substrates such as metal.
U.S. Pat. No. 5,268,404 to Mowrey discloses a one-part adhesive composition exhibiting strong rubber-to-metal bonds with excellent environmental resistance without the necessity of first priming the metal surface. The composition comprises a halogenated polyolefin, an aromatic nitroso compound, metal oxide such as zinc oxide or magnesium oxide, and optionally a vulcanizing agent such as sulfur or selenium, a phenolic epoxy resin, or carbon black.
U.S. Pat. No. 5,432,246 to Fenn et al. discloses a silane oligomer made from a secondary amino-alkoxy silane, a polyisocyanate and optionally a single isocyanate group, resulting in a substituted urea, with no free remaining isocyanate groups.
U.S. Pat. No. 6,512,039 to Mowrey discloses an adhesive designed to bond metal to peroxide cured elastomers. A representative formulation comprises from 10 to 20% of chlorosulfonated polyethylene, from 15-25% of an acid scavenger, from 35-45% of a polymaleimide, from 5-15% of precipitated silica, and 10-20% of an isocyanatosilane.
EP 0187171 discloses primers for thermoplastic polyolefins. Representative of these primer is a composition comprising chlorinated polyolefin, such as polypropylene, or graft-modified polypropylene, a crosslinkable binder and a crosslinking agent from selected from amines, amidoamines, isocyanates, poly-isocyanates, cyanurates, and acrylates containing —OH or —COOH groups.
Representative adhesives containing polyisocyanates, or bonding agents such as aminosilanes are known. U.S. Pat. No. 4,031,120 (Lord) discloses one-coat adhesives based on isocyanatosilane or an isocyanate-organosilane adduct. A variety of film formers are suggested. Optimally, the adhesive combines a nitroso compound. It would be industrially important to provide good primary adhesion bonding of a one-coat adhesive to more than one type of TPE under conditions of limited heat, such as extrusion bonding or cladding, or insert injection molding.